1. Field of the Invention
The present invention relates generally to ink jet printers, and more particularly, to an ink jet printer capable of smoothing images.
2. Description of the Related Art
There are known some ink jet printers using a piezoelectric element (PZT) for a print head. In such a print head, pulse voltage corresponding to image data is applied to the piezoelectric element, and the piezoelectric element deforms in response to the application of the pulse voltage, which pressurizes ink within a prescribed container (ink channel) and permits ink droplets to be ejected from a nozzle provided at the ink channel toward a recording sheet. An image based on the image data is formed on the recording sheet by the ejected ink droplets.
In the ink jet printer, the amount of liquid to form ink droplets to be ejected is adjusted by causing degree of distortion at the piezoelectric element by changing the amplitude of the pulse voltage applied to the piezoelectric element. Thus adjusting the amount of liquid to form ink droplets, a plurality of dot sizes are available for ink to stick to a recording sheet. Among the plurality of dot sizes, larger dot sizes are used to represent a dark part of an image, and smaller sizes are used to represent a light part of the image.
Meanwhile, in the field of ink jet printers, a smoothing process of virtually improving the resolution of an image and improving a jaggy part of the image at the time of reproducing the image from image data is performed. In the smoothing process, smaller size dots as described above are used.
Referring to FIGS. 29 and 30, the smoothing process will be described. FIG. 29 is a diagram for use in illustration of printing of an image by a normal ink jet printer.
An image printed by the ink jet printer is virtually divided into segments, dots 251 to 254 having a plurality of sizes as described above are printed for printing an image having a density. In the image, the dot center-to-center distance, the distance between the center of a certain dot and the center of an adjacent dot in the four sides is fixed regardless of the size of the dots. In the conventional ink jet printer thus printing images performs the following smoothing process.
FIG. 30 is a diagram for use in illustration of a smoothing process by a conventional ink jet printer.
In the conventional ink jet printer, an image segmented into a lattice is subjected to a smoothing process, in which smaller size smoothing dots 256 are printed around a normal size dot 255.
If, however, smaller size dots are printed in the smoothing process as described above, the dot center-to-center distance may appear to be separated in some printed images. In such an image, the effect of smoothing process deteriorates, in other words, high definition image is not available to the user.